The problem area on which the present invention is based can best be discussed with reference to the accompanying FIGS. 1 to 3. Thus, in modern LED lighting systems, use is increasingly being made of a multiplicity of parallel-connected LED modules 10a, 10b, etc., which are operated from a domestic power supply system, which provides the voltage UN, via a central electronic ballast 12. UN is 230 V AC, for example, in Germany. The electronic ballast 12 provides a voltage UE at its output, which voltage can be 24 V DC, for example. In this case, the electronic ballast 12 is generally short circuit-proof and equipped with a current monitoring system that triggers in the event of overcurrent. After the removal of a possible short circuit on the secondary circuit the electronic ballast 12 starts up again independently. In order to avoid unintended malfunctions of the system, for example switching off, flicker or periodic flashing during operation, the switch-on current of the parallel-connected LED modules 10a, 10b must not reach the overcurrent switch-off threshold of the electronic ballast 12.
FIG. 2 shows the temporal profile of the input voltage UE of the light modules 10a, 10b known from the prior art, and also the temporal profile of the input current IE for a selected one of said light modules 10a, 10b. It is established here that the maximum switch-on current IE is 300 mA approximately 2.20 ms after switch-on. In continuous operation, the current TE is only 76 mA. On account of this high switch-on current, the maximum permissible number of light modules 10a, 10b operated in parallel from an electronic ballast 12 has to be severely limited.
FIG. 3 shows by way of example in a schematic illustration the construction of one of these LED modules 10 known from the prior art. This LED module comprises an input having a first E1 and a second E2 input terminal. This is followed by a filter device 14 comprising an inductance L1 and a capacitor C1. The filter device 14 has the terminals FE1 and FE2 on the input side and the terminals FA1 and FA2 on the output side. The filter device 14 is followed by a DC-DC converter 16 having input terminals DCE1 and DCE2 and output terminals DCA1 and DCA2. The filter device 14 serves for ensuring high-frequency decoupling between the electronic ballast 12 and the DC-DC converter 16 in order to avoid EMC interference. The output terminals DCA1 and DCA2 simultaneously form the output terminals A1 and A2 of the LED module 10. By way of example, an LED 18 is connected thereto. In this case, the LED 18 can be arranged on the same circuit board as the rest of the circuit, but provision can also be made for leading out the terminals A1, A2 from the circuit board on which the LED module 10 is realized, in order to couple a separately arranged LED 18 to the LED module 10. In this case, the switch-on current IE is essentially limited by the inductance L1 and the nonreactive resistance of said inductance L1. This furthermore results in the disadvantage that the operating current brings about a voltage drop at the nonreactive resistance of the inductance L1 and, consequently, permanent losses and additional heating occur in the LED module 10.